I just finished a ballast install on my boat over the weekend... a Fly High integrated bow sack under the seats of my 2007 Supra 22 walkthrough (without the playpen). I liked the idea of pulling off a thru-hull that's already there, until I heard of people starving their intake and running up the thermostat. I didn't like the idea of that at all...
I had never done this before, had no idea what I was doing, but worked through it slowly... once I got my hands dirty, it took about 15 hours by myself. Having a buddy would have probably cut that in half, if not more.
I wanted to do it right, but my god was it expensive... I used a reversible Jabsco Ballast puppy pump, reinforced tubing, 3 check-valves, brass and real stainless-steel thru-hulls, and brass elbow and ball valve. Flipped the switch for the first time yesterday afternoon and everything worked. But it cost $550 before bags.
I would be very curious to know what a shop would have charged me... it would have been worth a lot to me. But that being said, the project was very easy once you get into it.
I dewinterize in 2 weeks... can't wait to try out 2200 lbs of plumbed ballast!!